What is multiplication?Date: 11/09/97 at 18:32:10 From: JMTI Subject: What is multiplication? What does multiplication have to do with addition, geometry, and real life? Date: 01/14/98 at 12:35:55 From: Doctor Sonya Subject: Re: What is multiplication? I hope you've figured out what multiplication has to do with all these things by now, but in case you haven't, here's what I think. First, what does multiplication have to do with addition? What happens when you do something like multiply 3 times 4? (I'll write this as 3 * 4.) Well, 3 * 4 = 12, right? But ....... (drum-roll please) 3 + 3 + 3 + 3 = 12 too. So multiplying 3 by four is like adding 3 to itself 4 times. I think this is why we say "3 times 4", because you are taking 3 and adding it 4 times. What about 4 * 3? This means that we add 4 to itself 3 times: 4 + 4 + 4 = 12 which is what we should have gotten in the first place! Yay. In geometry, one thing you can use multiplication for is to calculate areas. For example, if you have a rectangle with one side that's 3 inches and the other that's 2 inches, what's the area? You find the area by multiplying the lengths of the two sides together. Finally, what does multiplication have to do with real life? Here are some of the areas where I use multiplication. 1. I multiply when I cook and have to double the recipe. 2. I multiply when I try to figure out how much interest I have earned on my savings account. 3. I multiply when I calculate how many cans of frozen lemonade to buy each week. (My family drinks about 1.5 cans a day, so for 7 days I need 1.5 * 7 = 10.5 cans. But what am I supposed to do with the extra half?) 4. Richard, who works in the Math Forum office here, says that he used multiplication recently when he wanted to find out how many bonds he needed to buy if he needed to make $1500 with interest. 5. Ken, also in the office, used multiplication to calculate how much money he'll make this year designing Web pages if he makes $200 per page. I hope this helps. Write us back if you have any more questions. -Doctor Sonya, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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